At present, evaporators are widely used in chemical, light industry, pharmaceutical, food and other industries. Evaporators are indispensable evaporation concentration and evaporation crystallization equipment in the current chemical industry. With the development of chemical industry technology, In order to cope with the needs of different wastewaters, different industries, and different materials, there are more and more types of evaporators, and their working principles and operating methods are also slightly different.
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1. Classification according to the residence condition of the solution in the evaporator:
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There are circulating evaporators and single-pass evaporators.
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1. Circulation evaporator
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In this type of evaporator, the solution circulates in the evaporator. The causes of circulation are different and the operations are different. They can be divided into two categories: natural circulation and forced circulation. Natural circulation evaporators are further divided into central circulation tube evaporators, hanging basket evaporators, Levin evaporators, and forced circulation evaporators.
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2. Single-pass evaporator
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The main feature of this type of evaporator is that the solution only passes through the heating chamber once in the evaporator, and the concentrated liquid is discharged without circulating flow. When the solution passes through the heating chamber, it flows in a film shape on the tube wall, so it becomes a liquid film evaporator. According to different material flow directions, single-pass evaporators are divided into rising film evaporators, falling film evaporators, and scraper evaporators.
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2. Classification by evaporation method
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1. Natural evaporation: That is, the solution evaporates at a temperature lower than the boiling point, such as seawater salt. In this case, because the solvent only vaporizes on the surface of the solution, the solvent vaporization rate is low.
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2. Boiling evaporation: Heating the solution to the boiling point makes it evaporate in the boiling state. Industrial evaporation operations are basically of this type.
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3. Classification according to evaporator operating pressure
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Evaporators are divided according to operating pressure and can be divided into normal pressure, pressurized and reduced pressure (vacuum) evaporation operations.
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Generally, heat-sensitive materials, such as antibiotic solutions, fruit juices, etc., should be processed under reduced pressure. High-viscosity materials should be evaporated using pressurized high-temperature heat sources (such as thermal oil, molten salt, etc.).
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4. Classification by evaporator efficiency number
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Can be divided into single-effect and multiple-effect evaporation. If the secondary steam generated by evaporation is directly condensed and no longer used, it is called single-effect evaporation. If the secondary steam is used as the next effect heating steam and multiple evaporators are connected in series, the evaporation process is called multiple effect evaporation.
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5. Classification according to evaporation process mode
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According to the process mode of evaporation, it can be divided into intermittent evaporation and continuous evaporation. Intermittent evaporation refers to the evaporation operation of feeding or discharging materials in batches. The characteristic of intermittent operation is that during the entire process, the concentration and boiling point of the solution in the evaporator change with time, so intermittent evaporation is an unsteady-state operation. Generally, intermittent evaporation is suitable for small-scale and multi-variety occasions, while continuous evaporation is suitable for large-scale production processes.
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Different types of evaporators are used in different environments, and each has its own advantages. There are many types of evaporators. When we choose to use an evaporator, we must consider the structure and operation and maintenance of the evaporator based on the on-site material conditions and provide a suitable evaporator for the customer.
